1. Technical Field
The invention relates to printing. More particularly, the invention relates to a method and apparatus for thermal expansion based print head alignment.
2. Description of the Background Art
Aligning large numbers of print heads is time consuming and/or costly. Print heads are currently aligned within the printer using precision mechanical references, manually adjusted by mounts, or adjusted by motors. Initially, the carriage plates the support the print heads must be machined very accurately to place the print heads exactly where they should be. Doing so is expensive and not always as accurate as required. Further, variability in manufacturing the print heads themselves means the print heads are not always positioned where they need to be. The state of the art provides an adjustment screw. The operator manually turns the screw to push the print heads forward or back. This procedure is very time consuming. After making such adjustment, the operator prints a pattern, inspects it, and measures it with a microscope. Then the operator makes another adjustment. This procedure is repeated, and typically four hours or more have elapsed before the alignment is done.
Some alignment techniques attempt to use thermal expansion to compensate for print head movement during operation. That is, the print heads are intentionally misaligned during manufacture to allow them to move into alignment when they are at an operating temperature in the field. For example, see U.S. Pat. No. 6,793,323, Thermal Expansion Compensation for Modular Printhead Assembly, U.S. Pat. No. 7,090,335, Thermal Expansion Compensation for Printhead Assembly, and U.S. Pat. No. 7,810,906, Printhead Assembly Incorporating Heat Aligning Printhead Modules. Such approach leaves much to serendipity because operating conditions vary widely in the field and no mechanism is provided for realigning the print heads if they are out of alignment in the field when at an operating temperature.
It would be advantageous to provide a mechanism that addresses the problem of aligning print heads in the field, and that allows such alignment to be performed as needed without the need for time consuming and/or costly procedures.